The European Union must stop taking powers from Britain because the push for
an ever-closer political union “lies in the past”, Kenneth Clarke, the
minister without portfolio, has conceded.

Mr Clarke, the former chancellor and a noted Europhile, has backed a manifesto by the think tank British Influence, which sets out the reasons for Britain remaining in the European Union.

However, the manifesto, which is also supported by Danny Alexander, the Chief Secretary to the Treasury, and Lord Mandelson, the former Labour cabinet minister, calls on European leaders to recognise the aim of an “ever-closer union” is no longer relevant.

Mr Clarke has repeatedly spoken out about the dangers of the UK leaving the EU.

Last month he warned that Britain would be excluded from lucrative international deals in the event of an exit, meaning few jobs and higher prices in the shops.

The British Influence manifesto warns that leaving the EU would be a “historical error” and insists that “we can actively reboot the EU for the 21st century and project our economic and political reform agenda in and through Europe to the wider world”.

However, it adds: “At the same time, it should be recognised by EU leaders that the time for an 'ever closer union’ in every possible policy area lies in the past.”

The manifesto says that Britain “should lead the EU reform campaign from within, not threaten unilateral repatriation of powers”. “A number of areas should better be left to member states rather than the EU,” it adds.

David Cameron has pledged to renegotiate Britain’s relationship with the EU before offering voters an in-out referendum in 2017.

Mr Clarke, the co-president of British Influence, said: “This is a compelling and practical manifesto for a reformed Europe focused on growth and competitiveness.

“David Cameron has already showed what can be achieved in Europe through strong, determined leadership.”

Theresa May, the Home Secretary, is facing a clash with Conservative backbenchers in the Commons today over her plans to opt out of 130 EU measures on justice and home affairs, and retain 35, including the controversial European Arrest Warrant.

Tory MPs last week accused Mrs May of trying to “bounce” Parliament into accepting her plans.

Following a series of meetings with ministers and backbenchers, Mrs May shifted her position and said that MPs would now be given until October to examine the plans.

Three Commons select committees will now report on the issues before the Government starts negotiating with the EU over the justice measures.

This week Mrs May will also reject proposals from Brussels for a powerful pan-European prosecutor.

The European Commission wants to set up a cross-border prosecution body to “protect” the EU’s financial interests.

Mrs May said that the Government will “not participate” in either the planned new prosecutor’s office or a “European police force”.